What's an evap leak?

A P1456 is an overall EVAP System leak code for Honda. Below is a link with a small explanation of the EVAP System and what it does. This Code is triggered because when the Computer for your Emissions System ran its self test ( which it does every morning during cold start up ) the system did not hold vacuum properly. http://repairpal.com/evaporative-control-system A P1456 type of leak can be caused by several things, such as the Canister Purge Valve, a defective Fuel Cap, A Defective Vent Solenoid etc.